It has been customary to use a fluoride resin, such as polytetrafluoroethylene, which is highly resistant to chemicals and heat, in the piston rings fitted on the pistons which are slidably received in the cylinders of a swash-plate compressor for an automotive air conditioner. Since fluoride resins have a relatively poor wear property, carbon fibers are typically distributed in the fluoride resins to improved their wear properties. The cylinders typically consist of aluminum alloys containing primary crystal silicon particles distributed therein to reduce the tendency of the carbon fibers to attack the cylinder surfaces.
However, in order to have primary crystal silicon to precipitate in an aluminum alloy, the silicon content of the alloy has to be increased and the material cost is thereby increased. Further, primary crystal silicon particles have relatively large diameters in the order of 50 to 500 micrometers and have a high hardness in the order of 1,000 Hv, making the aluminum alloy unsuitable for machining. Due to the tendency of the primary crystal silicon particles to produce cracks in the aluminum alloy and to peel off, a poor surface condition is produced, and the aluminum alloy tends to attack and wear out the other sliding member.